Intravascular stent

ABSTRACT

A stent in a non-expanded state has a first column expansion strut pair. A plurality of the first column expansion strut pair form a first expansion column. A plurality of second column expansion strut pair form a second expansion column. A plurality of first serial connecting struts form a first connecting strut column that couples the first expansion column to the second expansion column. The first expansion column, the second expansion column, and the first connecting strut column form a plurality of geometric cells. At least a portion of the plurality are asymmetrical geometric cells.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/824,142,filed Mar. 26, 1997, now U.S. Pat. No. 6,241,760 B1 which claimspriority to provisional application No. 60/017,484, filed Apr. 26, 1996.

This application claims the benefit of Provisional Patent ApplicationNo. 60/017,484 filed Apr. 26, 1996, the disclosure of which isincorporated by reference. This application is related to U.S. patentapplication Ser. No. 08/824,866, filed Mar. 26, 1997, entitled“Intravascular Stent” and U.S. patent application Ser. No. 08/824,865,filed Mar. 26, 1997, entitled “Intravascular Stent” , both having samenamed inventor G. David Jang and incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to intravascular stents, and more particularly toan intravascular stent which provides easy introduction through tortioussections of vessels.

2. Description of the Related Art

Angioplasty, either coronary or general vascular, has advanced to becomethe most effective means for revascularization of stenosed vessels. Inthe early 1980's, angioplasty first became available for clinicalpractice in the coronary artery, and has since proven an effectivealterative to conventional bypass graft surgery. Balloon catheterdependent angioplasty has consistently proven to be the most reliableand practical interventional procedure. Other ancillary technologiessuch as laser based treatment, or directional or rotational arthrectomy,have proven to be either of limited effectiveness or dependent onballoon angioplasty for completion of the intended procedure. Restenosisfollowing balloon-based angioplasty is the most serious drawback and isespecially prevalent in the coronary artery system.

Many regimens have been designed to combat restenosis, with limitedsuccess, including laser based treatment and directional or rotationalarthrectomy. Intravascular stenting, however, noticeably reduces therestenosis rate following angioplasty procedures. The procedure forintravascular stent placement typically involves pre-dilation of thetarget vessel using balloon angioplasty, followed by deployment of thestent, and expansion of the stent such that the dilated vessel walls aresupported from the inside.

The intravascular stent functions as scaffolding for the lumen of avessel. The scaffolding of the vessel walls by the stent serve to: (a)prevent elastic recoil of the dilated vessel wall, (b) eliminateresidual stenosis of the vessel; a common occurrence in balloonangioplasty procedures, © maintain the diameter of the stented vesselsegment slightly larger than the native unobstructed vessel segmentsproximal and distal the stented segment and (d) as indicated by thelatest clinical data, lower the restenosis rate. Following anangioplasty procedure, the restenosis rate of stented vessels has provensignificantly lower than for unstented or otherwise treated vessels;treatments include drug therapy and other methods mentioned previously.

Another benefit of vessel stenting is the potential reduction ofemergency bypass surgery arising from angioplasty procedures. Stentinghas proven to be effective in some cases for treating impending closureof a vessel during angioplasty. Stenting can also control and stabilizean unstable local intimal tear of a vessel caused by normal conductduring an angioplasty procedure. In some cases, an incomplete or lessthan optimal dilatation of a vessel lesion with balloon angioplasty cansuccessfully be opened up with a stent implant.

Early in its development, the practice of stenting, especially incoronary arteries, had serious anticoagulation problems. However,anticoagulation techniques have since been developed and are becomingsimpler and more effective. Better and easier to use regimens arecontinuously being introduced, including simple outpatientanticoagulation treatments, resulting in reduced hospital stays forstent patients.

An example of a conventional stent patent is U.S. Pat. No. 5,102,417(hereafter the Palmaz Patent). The stent described in the Palmaz Patentconsists of a series of elongated tubular members having a plurality ofslots disposed substantially parallel to the longitudinal axis of thetubular members. The tubular members are connected by at least oneflexible connector member.

The unexpanded tubular members of the Palmaz Patent are overly rigid sothat practical application is limited to short lengths. Even withimplementation of the multilink design with flexible connector membersconnecting a series of tubular members, longer stents can not navigatetortuous blood vessels. Furthermore, the rigidity of the unexpandedstent increases the risk of damaging vessels during insertion.Foreshortening of the stent during insertion complicates accurateplacement of the stent and reduces the area that can be covered by theexpanded stent. There is, further, no method of programming the stentdiameter along its longitudinal axis to achieve a tapered expandedstent, and no method of reenforcement of stent ends or other regions isprovided for.

Another example of a conventional stent patent is WO 96/03092, the Brunpatent. The stent described in the Brun patent is formed of a tubehaving a patterned shape, which has first and second meander patterns.The even and odd first meander patterns are 180 degrees out of phase,with the odd patterns occurring between every two even patterns. Thesecond meander patterns run perpendicular to the first meander patterns,along the axis of the tube.

Adjacent first meander patterns are connected by second meander patternsto form a generally uniform distributed pattern. The symmetricalarrangement with first and second meander patterns having sharp rightangled bends allows for catching and snagging on the vessel wall duringdelivery. Furthermore, the large convolutions in the second meanderpattern are not fully straightened out during expansion reducingrigidity and structural strength of the expanded stent. There is,further, no method of programming the stent diameter along itslongitudinal axis to achieve a tapering stent design, and no method ofreenforcement of stent ends or other regions is provided for.

These and other conventional stent designs suffer in varying degreesfrom a variety of drawbacks including: (a) inability to negotiate bendsin vessels due to columnar rigidity of the unexpanded stent; (b) lack ofstructural strength, radial and axial lateral, of the unexpanded stent;© significant foreshortening of the stent during expansion; (d) limitedstent length; (e) constant expanded stent diameter; (f) poor crimpingcharacteristics; and (g) rough surface modulation of the unexpandedstent.

There is a need for a stent with sufficient longitudinal flexibility inthe unexpanded state to allow for navigation through tortuous vessels.There is a further need for a stent that is structurally strong in theunexpanded state such that risk of damage or distortion during deliveryis minimal. A further need exists for a stent that maintainssubstantially the same longitudinal length during expansion to allowgreater coverage at the target site and simplify proper placement of thestent. Yet a further need exists for a stent design with sufficientlongitudinal flexibility that long stents of up to 100 mm can be safelydelivered through tortuous vessels. There is a need for a stent that isconfigured to expand to variable diameters along its length, such that ataper can be achieved in the expanded stent to match the natural taperof the target vessel. A need exists for a stent which, (i) can becrimped tightly on the expansion balloon while maintaining a low profileand flexibility, (ii) has a smooth surface modulation when crimped overa delivery balloon, to prevent catching and snagging of the stent on thevessel wall during delivery or (iii) with reenforcment rings on the endsor middle or both to keep the ends of the stent securely positionedagainst the vessel walls of the target blood vessel.

SUMMARY OF THE INVENTION

Accordingly an object of the present invention is to provide a scaffoldfor an interior lumen of a vessel.

Another object of the invention is to provide a stent which preventsrecoil of the vessel following angioplasty.

A further object of the invention is to provide a stent that maintains alarger vessel lumen compared to the results obtained only with balloonangioplasty.

Yet another object of the invention is to provide a stent that reducesforeshortening of a stent length when expanded.

Another object of the invention is to provide a stent with increasedflexibility when delivered to a selected site in a vessel.

A further object of the invention is to provide a stent with a lowprofile when crimped over a delivery balloon of a stent assembly.

Yet a further object of the invention is to provide a stent with reducedtupeling of the vessel wall.

Another object of the invention is to provide a chain mesh stent thatreduces vessel “hang up” in a tortious vessel or a vessel withcurvature.

These and other objects of the invention are achieved in a stent in anon-expanded state with a first column expansion strut pair. A pluralityof the first column expansion strut pair form a first expansion column.A plurality of second column expansion strut pair form a secondexpansion column. A plurality of first serial connecting struts form afirst connecting strut column that couples the first expansion column tothe second expansion column. The first expansion column, the secondexpansion column, and the first connecting strut column form a pluralityof geometric cells. At least a portion of the plurality are asymmetricalgeometric cells.

In another embodiment, at least a portion of the first connecting strutsinclude a proximal section, a distal section a first linear section anda first slant angle.

It yet another embodiment, a first expansion strut in the firstexpansion column is circumferentially offset from a corresponding secondexpansion strut of the second expansion column.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side elevation view of the pre-expansion mode of anembodiment of the stent of the present invention;

FIG. 1B is a cross sectional view of an embodiment of the stent of thepresent invention;

FIG. 1C is a longitudinal cross sectional view of an embodiment of thestent of the present invention,

FIG. 2A is a scale drawing of the strut pattern of an embodiment of thestent of the present invention.

FIG. 2B is an expanded view of a section of the pattern of FIG. 2A.

FIG. 3A is a schematic illustration of a the pre-expansion mode of anembodiment of the stent of the present invention.

FIG. 3B is a schematic illustration of the post-expansion mode of anembodiment of the stent of the present invention.

FIG. 4A is a scale drawing including dimensions of an embodiment of thestent of the present invention.

FIG. 4B is an enlarged section of the scale drawing of FIG. 4A.

FIG. 5 is a scale drawing of an embodiment of the stent of the presentinvention with a tapered diameter in its post-expansion mode.

FIG. 6A is a scale drawing of an embodiment of the stent of the presentinvention with reenforcment expansion columns.

FIG. 6B is a perspective view of the embodiment of FIG. 6A.

FIG. 7A is a scale drawing of an embodiment of the stent of the presentinvention including relief notches at strut joints to increaseflexibility of the joints.

FIG. 7B is an enlarged region of the embodiment of FIG. 7A.

FIG. 7C is an enlarged view of a single connecting strut joining twoexpansion strut pairs in accordance with the embodiment of FIG. 7A.

FIG. 8A is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention.

FIG. 8B is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention.

FIG. 8C is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention.

FIG. 8D is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention.

FIG. 8E is a drawing of an alternate geometry of connecting struts andjoining struts in accord with the present invention.

FIG. 9 is a delivery balloon catheter, illustrating a method of deliverof a stent in accord with the present invention.

DETAILED DESCRIPTION

A first embodiment of the present invention is shown in FIGS. 1A, 1B,1C, 2A and 2B. Referring to FIG. 1A, an elongate hollow tubular stent 10in an unexpanded state is shown. A proximal end 12 and a distal end 14define a longitudinal length 16 of stent 10. The longitudinal length 16of the stent 10 can be as long as 100 mm or longer. A proximal opening18 and a distal opening 20 connect to an inner lumen 22 of stent 10.Stent 10 can be a single piece, without any seams or welding joints ormay include multiple pieces.

Stent 10 is constructed of two to fifty or more expansion columns orrings 24 connected together by interspersed connecting strut columns 26.The first column on the proximal end 12 and the last column on thedistal end 14 of stent 10 are expansion columns 24.

Expansion columns 24 are formed from a series of expansion struts 28,and joining struts 30. Expansion struts 28 are thin elongate membersarranged so that they extend at least in part in the direction of thelongitudinal axis of stent 10. When an outward external force is appliedto stent 10 from the inside by an expansion balloon or other means,expansion struts 28 are reoriented such that they extend in a morecircumferential direction, i.e. along the surface of cyllindrical stent10 and perpendicular to its longitudinal axis. Reorientation ofexpansion struts 28 causes stent 10 to have an expanded circumferenceand diameter. In FIG. 1A, expansion struts 28 of unexpanded stent 10 areseen to extend substantially parallel to the longitudinal axis of stent10.

Expansion struts 28 are joined together by joining struts 30 to form aplurality of expansion strut pairs 32. Expansion strut pairs have aclosed end 34 and an open end 36. Additional joining struts 30 jointogether expansion struts 28 of adjacent expansion strut pairs 32, suchthat expansion struts 28 are joined alternately at their proximal anddistal ends to adjacent expansion struts 28 to form expansion columns24. Each expansion column 24 contains a plurality, typically eight totwenty, twenty to sixty, or larger of expansion struts 28.

Connecting struts 38 connect adjacent expansion columns 24 forming aseries of interspersed connecting strut columns 26 each extending aroundthe circumference of stent 10. Each connecting strut 38 joins a pair ofexpansion struts 28 in an expansion column 24 to an adjacent pair ofexpansion struts 28 in an adjacent expansion column 24. For stent 10 ofFIG. 1A, the ratio of expansion struts 28 in an expansion column 24 toconnecting struts 38 in a connecting strut column 26 is two to one;however, this ratio in general can be x to 1 where x is greater or lessthan two. Furthermore, since the stent 10 of FIG. 1A begins with anexpansion column 24 on the proximal end 12 and ends with an expansioncolumn 24 on the distal end 14, if there are n expansion columns 24 withm expansion struts 28 per column, there will be m−1 connecting strutcolumns 26, and n(m−1)/2 connecting struts 38.

The reduced number of connecting struts 38 in each connecting strutcolumn 26, as compared to expansion struts 28 in each expansion column24, allows stent 10 to be longitudinally flexibility. Longitudinalflexibility can be further increased by using a narrow width connectingstrut, providing additional flexibility and suppleness to the stent asit is navigated around turns in a natural blood vessel.

At least a portion of the open spaces between struts in stent 10 formasymmetrical cell spaces 40. A cell space is an empty region on thesurface of stent 10, completed surrounded by one or a combination ofstent struts, including expansion struts 28, connecting struts 38, orjoining struts 30. Asymmetrical cell spaces 40 are cell spaces whichhave no geometrical symmetry i.e. no rotation, reflection, combinationrotation and reflection or other symmetry.

Asymmetrical cell spaces 40 in FIG. 1A are surrounded by a firstexpansion strut pair 32 in a first expansion column 24, a firstconnecting strut 38, a second expansion strut pair 32 in an adjacentexpansion column 24, a first joining strut 30, a second connecting strut38, and a second joining strut 30. Furthermore, expansion strut pairs 32of asymmetrical cell space 40 may be circumferentially offset i.e. havelongitudinal axes that are not collinear and have their open ends 36facing each other. The space between two expansion struts of anexpansion strut pair 32 is known as a loop slot 42.

FIG. 1B shows inner lumen 22, radius 44 and stent wall 46 of stent 10.Stent wall 46 consists of stent struts including expansion struts 28,connecting struts 38 and joining struts 30.

FIG. 1C shows, proximal end 12, distal end 14, longitudinal length 16,inner lumen 22, and stent wall 46 of stent 10. Inner lumen 22 issurrounded by stent wall 46 which forms the cyllindrical surface ofstent 10.

Referring now to FIGS. 2A and 2B, joining struts 30 of stent 10 are seento extend at an angle to the expansion struts 28, forming a narrow angle48 with one expansion strut 28 in an expansion strut pair 32 and a wideangle 50 with the other expansion strut 28 of an expansion strut pair32. Narrow angle 48 is less than ninety degrees, while wide angle 50 isgreater than ninety degrees. Joining struts 30 extend bothlongitudinally along the longitudinal axis of stent 10 andcircumferentially, along the surface of the stent 10 perpendicular itslongitudinal axis.

Expansion strut spacing 52 between adjacent expansion struts 28 in agiven expansion column 24 are uniform in stent 10 of FIGS. 2A and 2B;however, non-uniform spacings can also be used. Expansion strut spacings52 can be varied, for example, spacings 52 between adjacent expansionstruts 28 in an expansion column 24 can alternate between a narrow and awide spacing. Additionally, spacings 52 in a single expansion column 24can differ from other spacings 52 in other columns 24.

It is noted that varying expansion strut spacings 52 which form the loopslots 42 results in variable loop slot widths. Furthermore, thelongitudinal axis of the loop slots 42 need not be collinear or evenparallel with the longitudinal axis of loop slots 42 of an adjacentexpansion column 24. FIGS. 2A and 2B show an arrangement of expansionstruts 28 such that collinear, parallel adjacent loop slots 42 areformed, but non-collinear and non-parallel loop slots 42 can also beused.

Additionally the shape of loop slots 42 need not be the same among loopslots of a single or multiple expansion columns 24. The shape a loopslots 42 can be altered by changing the orientation or physicaldimensions of the expansion struts 28 and/or joining struts 30 whichconnect expansion struts 28 of expansion strut pairs 32 defining theboundaries of loop slots 42.

Connecting struts 38 couple adjacent expansion columns 24, by connectingthe distal end of an expansion strut pair in one expansion column 24 tothe proximal end of an adjacent expansion strut pair 32 in a secondexpansion column 24. Connecting struts 38 of FIGS. 2A and 2B are formedfrom two linear sections, a first linear section 54 being joined at itsdistal end to a second linear section 56 at its proximal end to form afirst slant angle 58.

The first linear section 54 of a connecting strut 38 is joined toexpansion strut 28 at the point where joining strut 30 makes narrowangle 48 with expansion strut 28. First linear section 54 extendssubstantially collinear to joining strut 30 continuing the line ofjoining strut 30 into the space between expansion columns 24. The distalend of the first linear section 54 is joined to the proximal end of thesecond linear section 56 forming slant angle 58. Second linear section56 extends substantially parallel to expansion struts 28 connecting atits distal end to joining strut 30 in an adjacent expansion column 24.The distal end of second linear section 56 attaches to expansion strut28 at the point where joining strut 30 makes narrow angle 48 withexpansion strut 28. Further, joining strut 30 can have a second slantangle with a width that can be the same or different from the width ofthe first slant angle.

FIGS. 2A and 2B show connecting struts 38 and joining struts 30 slantedrelative to the longitudinal axis of stent 10, with the circumferentialdirection of the slanted struts alternating from column to adjacentcolumn. Circumferential direction refers to the handedness with whichthe slanted struts wind about the surface of the stent 10. Thecircumferential direction of the slant of connecting strut first linearsections 54 in a connecting strut column 26 is opposite thecircumferential direction of the slant of connecting strut first linearsections 54 in an adjacent connecting strut column 26. Similarly, thecircumferential direction of the slant of joining struts 30 in anexpansion column 24 is opposite the circumferential direction of theslant of joining struts 30 in an adjacent expansion column 24.Alternating circumferential slant directions of connecting struts 38 andjoining struts 30 prevents axial warping of stent 10 during deliver andexpansion. Other non-alternating slant direction patterns can also beused for connecting struts 38 or joining struts 30 or both.

FIG. 3A and 3B show a schematic illustration of a stent design accordingto the present invention in an unexpanded and expanded staterespectively. The design is depicted as a flat projection, as if stent10 were cut lengthwise parallel to its longitudinal axis and flattenedout. The connecting struts 38 consist of first and second linearsections 54 and 56 forming slant angle 58 at pivot point 60. Anasymmetrical cell space 40 is formed by expansion strut pairs 32,connecting struts 38 and joining struts 30. Multiple interlockingasymmetrical cell spaces 40 make up the design pattern.

As the stent is expanded, see FIG. 3B, the expansion strut pairs 32spread apart at their open ends 36, shortening the length of expansionstruts 28 along the longitudinal axis of the cylindrical stent. Thelongitudinal shortening of expansion struts 28 during expansion iscountered by the longitudinal lengthening of connecting struts 38. Thewidening of slant angle 58 during expansion straightens connectingstruts 38 and lengthens the distance between the coupled expansion strutpairs 32. The lengthening of the distance between coupled expansionstrut pairs 32 substantially compensates for the longitudinal shorteningof expansion struts 28. Thus, the stent has substantially constantunexpanded and expanded longitudinal lengths.

When the stent is expanded, each expansion column 24 becomescircumferentially stretched, enlarging the space between struts. Theinterlinking of expansion columns 24 by connecting struts 38 that havebeen straightened through the expansion process gives the stent 10 ahigh radial support strength. The entire stent 10 when expanded isunitized into a continuous chain mesh of stretched expansion columns 24and connecting strut columns 26 forming an asymmetrical interlockingcell geometry which resists collapse both axially and radially. When thestent is expanded it has increased rigidity and fatigue tolerance.

In addition, efficient bending and straightening of connecting struts 38at pivot points 60 allows increased longitudinal flexibility of thestent. For the stent to bend longitudinally, at least some of connectingstruts 38 are forced to bend in their tangent plane. The tangent planeof a specific connecting strut 38 refers to the plane substantiallytangent to the cyllindrical surface of the stent at that connectingstrut 38. The width of connecting struts 38 is typically two to four, ormore times the thickness, which makes connecting struts 38 relativelyinflexible when bending in their tangent plane. However, pivot points 60in connecting struts 38 provide connecting struts 38 a flexible jointabout which to more easily bend increasing longitudinal flexibility ofthe stent.

Referring to FIGS. 4A and 4B, a variation of the first embodiment ofstent 10 of the present invention is shown. In this variation, stent 10has a length 16 of 33.25 mm and an uncrimped and unexpandedcircumference 88 of 5.26 mm. Fifteen expansion columns 24 areinterspersed with connecting strut columns 26. Each expansion column 24consists of twelve expansion struts 28 joined alternately at theirproximal and distal ends by joining struts 30 forming six expansionstrut pairs 32. Expansion struts 28 are aligned parallel to thelongitudinal axis of cylindrical stent 10. Joining struts 30 form anarrow angle 48 and a wide angle 50 with the respective expansion struts28 of expansion strut pairs 32. Adjacent expansion columns 24 employalternating circumferential slant directions of joining struts 30.

In this variation of the first embodiment, expansion strut width 62 is0.20 mm, expansion strut length 64 is 1.51 mm, and connecting strutwidth 66 is 0.13 mm. Distance 68 from the outer edge of a firstexpansion strut 28 to the outer edge of a second adjacent expansionstrut 28 in the same expansion column 24 is 0.64 mm, leaving a loop slotwidth 70 of 0.24 mm.

In this variation of the first embodiment, connecting struts 38 consistof a slanted first linear section 54 joined to a second linear section56 at a slant angle 58. First linear section 54 is slightly longer thansecond linear section 56 and is attached at its proximal end to anexpansion strut 28 in an expansion column 24. The attachment of theproximal end of first linear section 54 to expansion strut 28 is at thepoint where joining strut 30 makes narrow angle 48 with expansion strut28. First linear section 54 extends substantially collinear to joiningstrut 30 attaching at its distal end to the proximal end of secondlinear section 56 to form slant angle 58. Second linear section 56extends substantially collinear to expansion struts 28, attaching at itsdistal end to an expansion strut 28 in an adjacent expansion column 24.The attachment occurs at the point where expansion strut 28 forms narrowangle 48 with joining strut 30. Joining struts 30 and connecting strutfirst linear sections 54 slant in alternating circumferential directionsfrom column to adjacent column.

The joining of connecting struts 38 and expansion struts 28 at the pointwhere narrow angle 48 is formed aids smooth delivery of stent 10 bystreamlining the surface of the unexpanded stent and minimizing possiblecatching points. Bare delivery of stent 10 to the target lesion in avessel will thus result in minimal snagging or catching as it isnavigated through turns and curvatures in the vessel. Stent 10 behaveslike a flexible, tubular sled as it is moved forward or backward in thevessel on the delivery catheter, sliding through tortuous vessels andover irregular bumps caused by atherosclerotic plaques inside the vessellumen.

When fully expanded Stent 10 of FIGS. 4A and 4B has an internal diameterof up to 5.0 mm, while maintaining an acceptable radial strength andfatigue tolerance. The crimped stent outer diameter can be as small as1.0 mm or less depending on the condition of the underlying deliveryballoon profile; A small crimped outer diameter is especially importantif stent delivery is to be attempted without predilation of the targetsite. When the stent is optimally crimped over the delivery balloon, thesurface of the crimped stent is smooth allowing for no snagging of thestent struts during either forward or backward movement through avessel.

FIG. 5 shows a second embodiment of the present invention in which thestent 10 in its expanded form has a gradual taper from proximal end 12to distal end 14. The shaded segments 72, 74, 76, 78, 80, 82 and 84 ofexpansion struts 28 represent regions of expansion struts 28 to beremoved. Removal of the shaded segments 72, 74, 76, 78, 80, 82 and 84provides stent 10 with a gradual taper when expanded with distal end 14having a smaller expanded diameter than proximal end 12. The degree ofshortening of the expanded diameter of the stent 10 at a given expansioncolumn 24 will be proportional to the length of the removed segment 72,74, 76, 78, 80, 82, or 84 at that expansion column 24. In the expandedstent 10 the shortened expansion struts 28 will have a shortenedcomponent along the circumference of the stent resulting in a shortenedcircumference and diameter. The tapered diameter portion can bepositioned anywhere along the length of stent 10, and the tapering canbe made more or less gradual by removing appropriately larger or smallerportions of the expansion struts 28 in a given expansion column 24.Tapering is especially important in long stents, longer than 12 mm,since tapering of blood vessels is more pronounced over longer lengths.A long stent with a uniform stent diameter can only be matched to thetarget vessel diameter over a short region. If the proximal vessel sizeis matched with the stent diameter, the expanded distal end of the stentwill be too large for the natural vessel and may cause an intimaldissection of the distal vessel by stent expansion. On the other hand,if the distal vessel size is matched with the stent diameter, theproximal end of the expanded stent will be too small to set inside thevessel lumen. It is therefore desirable to have a stent with a taperedexpanded diameter.

Another way achieve a tapered expanded stent is to change the stiffnessof the stent struts, expansion struts, connecting struts or joiningstruts such that the stiffness of the struts varies along the length ofthe stent. The stiffness of the struts can be changed by alteringlength, width or thickness, adding additional stiffening material, usinga chemical or mechanical means to alter the physical properties of thestent material, or applying one or a series of elastic elements aboutthe stent.

Along with the use of a tapered diameter stent, a matching taperedballoon catheter would ideally be made for delivery and deployment ofthe tapered diameter stent. The method of using a tapered matchingballoon catheter with a tapered diameter stent is within the scope ofthe present invention.

Using a tapered balloon to expand a non-tapered stent will also achievea tapered expanded stent; however, since no metal is removed from thestent, the stent is tapered as a result of incomplete expansion. Thestent will therefore have increased metal fraction at the tapered endresulting in increased risk of acute thrombosis. Metal fraction is theproportion of the surface of the expanded stent covered by the stentstrut material. Shortening the expansion struts as shown in FIG. 5allows for a tapered expanded stent with substantially constant metalfraction along its length.

A third embodiment of the present invention shown in FIGS. 6A and 6B hasmultiple reenforcement expansion columns 86 placed along the length ofthe stent 10. The reenforcement columns 86 are placed along the stentlength to provide additional localized radial strength and rigidity tostent 10. Additional strength and rigidity are especially important atthe ends of the stent to prevent deformation of the stent both duringdelivery and after placement. During delivery the stent ends can catchon the vessel wall possibly deforming the unexpanded stent and alteringits expansion characteristics. After the stent has been placed it isimportant that the stent ends are rigid so that they set firmly againstthe vessel wall; otherwise, during a subsequent catheter procedure, thecatheter or guidewire can catch on the stent ends pulling the stent awayfrom the vessel wall and possibly damaging and/or blocking the vessel.

The specific variation of the third embodiment of stent 10 depicted inFIGS. 6A and 6B has a length 16 of 20.70 mm and an uncrimped andunexpanded circumference 88 of 5.26 mm. The stent 10 consists of sixexpansion columns 24 and three reenforcement expansion columns 86, eachconsisting respectively of twelve expansion struts 28 or reenforcementexpansion struts 90. The reenforcement expansion columns 86 arepositioned one at either end, and one along the length of the stent 10.

The expansion strut width 62 is 0.15 mm, reenforcement expansion strutwidth 92 is 0.20 mm, and the connecting strut width 66 is 0.10 mm. Thenarrow angle 48 formed by joining strut 30 and expansion strut 28 is 75degrees, and the narrow angle 94 formed by reenforcement joining strut96 and reenforcement expansion strut 90 is 60 degrees.

Other arrangements of reenforcement expansion columns 86, such asproviding reenforcement expansion columns 86 only on the ends of thestent, only on one end, or at multiple locations throughout the lengthof the stent can also be used and fall within the scope of the presentinvention. A taper can also be programmed into the reenforced stent 10by shortening expansion struts 28 and reenforcement expansion struts 90in appropriate expansion columns 24 and 86.

A fourth embodiment of the present invention, shown in the FIGS. 7A, 7Band 7C, is similar to the third embodiment but has the added feature ofrelief notches 98 and 100. A relief notch is a notch where metal hasbeen removed from a strut, usually at a joint where multiple struts areconnected. Relief notches increase flexibility of a strut or joint bycreating a thinned, narrow region along the strut or joint. Relief notch98 is formed at the joint formed between first linear section 54 ofconnecting strut 38 and expansion strut 28. Relief notch 100 is formedat the joint between second linear section 56 of connecting strut 38 andexpansion strut 28. The positioning of the relief notches gives addedflexibility to the unexpanded stent. Relief notches can be placed atother joints and can be included in any of the previously mentionedembodiments.

FIGS. 8A, 8B, 8C, 8D and 8E illustrates some examples of alternateconnecting strut designs which can be used in any of the previouslydiscussed embodiments. FIG. 8A shows a rounded loop connecting strut 38which joins two circumferentially offset expansion strut pairs 32 inadjacent expansion columns. Expansion struts 28 in each expansion strutpair 32 are joined by a joining strut 30. Joining struts 30 are slantedsuch as to form a narrow angle 48 and a wide angle 50 with the expansionstruts 28 they connect. The rounded loop connecting strut 38 connectsexpansion struts 28 at the point where narrow angle is formed betweenexpansion strut 28 and joining strut 30. The slopes of the roundedconnecting strut 38 at its proximal end 102 and distal end 104substantially match the slopes of the joining struts 30 connecting thepairs of expansion struts 28. The rounded loop connecting strut 38 thusblends smoothly into the joining struts 30. Additionally the roundedloop connecting strut 38 has a first radius of curvature 106 and asecond radius of curvature 108.

In the design of FIG. 8B a rounded loop connecting strut 38 joins twocircumferentially offset expansion strut pairs 32 in adjacent expansioncolumns. Expansion struts 28 in each expansion strut pair 32 are joinedby a joining strut 30. Joining struts 30 are at right angles to theexpansion struts 28 they connect. The rounded loop connecting strut 38connects to expansion struts 28 at the same point as joining struts 30.The rounded connecting strut 38 has a first radius of curvature 106 anda second radius of curvature 108 such that it connects circumferentiallyoffset expansion strut pairs 32.

In the design of FIG. 8C connecting strut 38 joins two circumferentiallyoffset expansion strut pairs 32 in adjacent expansion columns. Expansionstruts 28 in each expansion strut pair 32 are joined by a joining strut30. Joining struts 30 are slanted such as to form a narrow angle 48 anda wide angle 50 with the expansion struts 28 they connect. Theconnecting strut 38 connects expansion struts 28 at the point wherenarrow angle 48 is formed between expansion strut 28 and joining strut30.

The connecting strut 38 is made up of three linear sections 110, 112,and 114 forming two slant angles 116 and 118. The proximal end ofsection 110 is attached to expansion strut 28 at the point where joiningstrut 30 forms narrow angle 48 with expansion strut 28. Section 110extends substantially collinear to joining strut 30 and is attached atits distal end to section 112 forming slant angle 116. Section 112extends at an angle to section 110 such that section 112 issubstantially parallel to expansion struts 28 and is connected at itsdistal end to the proximal end of section 114 forming slant angle 118.Section 114 extends at an angle such that it is substantially collinearto joining strut 30 of the adjacent expansion strut pair 32. Section 114attaches at its distal end to expansion strut 28 of the adjacentexpansion strut pair 32, at the point where joining strut 30 formsnarrow angle 48 with expansion strut 28.

In the design of FIGS. 8D and 8E a connecting strut 38 joins twocircumferentially offset expansion strut pairs 32 in adjacent expansioncolumns. Expansion struts 28 in each expansion strut pair 32 are joinedby a joining strut 30. Joining struts 30 are at right angles to theexpansion struts 28 they connect. The connecting strut 38 connects toexpansion struts 28 at the same point as joining struts 30.

The connecting struts 38 of FIGS. 8D and 8E are made up of multipleconnecting strut sections connected end to end to form a jaggedconnecting strut 38 with multiple slant angles, coupling expansion strutpair 32 to adjacent expansion strut pair 32. The connecting strut ofFIG. 8D is made up of three connecting strut sections 120, 122, and 124with two slant angles 126 and 128, while the connecting strut of FIG. 8Econsists of four connecting strut sections 130, 132, 134, and 136 withthree slant angles 138, 140 and 142. In addition, the connecting strutsection 134 can be modified by replacing connecting strut section 136 bythe dotted connecting strut section 144 to give another possiblegeometry of connecting struts 38.

One skilled in the art will recognize that there are many possiblearrangements of connecting struts and joining struts consistent with thepresent invention; the above examples are not intended to be anexhaustive list.

The stent of the present invention is ideally suited for application incoronary vessels although versatility in the stent design allows forapplications in non-coronary vessels, the aorta, and nonvascular tubularbody organs.

Typical coronary vascular stents have expanded diameters that range from2.5 to 5.0 mm. However, a stent with high radial strength and fatiguetolerance that expands to a 5.0 mm diameter may have unacceptably highstent metal fraction when used in smaller diameter vessels. If the stentmetal fraction is high, the chances of acute thrombosis and restenosispotential will increase. Even with the same metal fraction a smallercaliber vessel is more likely than a larger one to have a high rate ofthrombosis. It is, therefore, preferred to have at least two differentcategories of stents for coronary application, for example, smallvessels stents for use in vessels with diameters from 2.5 mm to 3.0 mm,and large vessel stents for use in vessels with diameters from 3.0 mm to5.0 mm. Thus, both small vessels and large vessels when treated with theappropriate sized stent will contain stents of similar idealized metalfraction.

The stent of the present invention can be made using a CAM-driven lasercutting system to cut the stent pattern from a stainless steel tube. Therough-cut stent is preferably electro-polished to remove surfaceimperfections and sharp edges. Other methods of fabricating the stentcan also be used such as EDM, photo-electric etching technology, orother methods. Any suitable material can be used for the stent includingother metals and polymers so long as they provide the essentialstructural strength, flexibility, biocompatibility and expandability.

The stent is typically at least partially plated with a radiopaquemetal, such as gold, platinum, tantalum or other suitable metal. It ispreferred to plate only both ends of the stent by localized plating;however, the entire stent or other regions can also be plated. Whenplating both ends, one to three or more expansion columns on each end ofthe stent are plated to mark the ends of the stent so they can beidentified under fluoroscopy during the stenting procedure. By platingthe stent only at the ends, interference of the radiopaque platingmaterial with performance characteristics or surface modulation of thestent frame is minimized. Additionally the amount of plating materialrequired is reduced, lowering the material cost of the stent.

After plating, the stent is cleaned, typically with detergent, salineand ultrasonic means that are well-known in the art. The stents are theninspected for quality control, assembled with the delivery ballooncatheter, and properly packaged, labeled, and sterilized.

The stent can be marketed as stand alone or as a pre-mounted deliveryballoon catheter assembly as shown in FIG. 9. Referring to FIG. 9, thestent 10 is crimped over a folded balloon 146 at the distal end 148 of adelivery balloon catheter assembly 150. The assembly 150 includes aproximal end adapter 152, a catheter shaft 154, a balloon channel 156, aguidewire channel 158, a balloon 146, and a guidewire 160. Balloon 146can be tapered in an expanded state, be curved from a proximal end to adistal end in the expanded state. Additionally stent 10 can benon-tapered or tapered in the expanded state.

Typically the guidewire 160 is inserted into the vein or artery andadvanced to the target site. The catheter shaft 154 is then forwardedover the guidewire 160 to position the stent 10 and balloon 146 intoposition at the target site. Once in position the balloon 146 isinflated through the balloon channel 156 to expand the stent 10 from acrimped to an expanded state. In the expanded state, the stent 10provides the desired scaffolding support to the vessel. Once the stent10 has been expanded, the balloon 146 is deflated and the catheter shaft154, balloon 146, and guidewire 160 are withdrawn from the patient.

The stent of the present invention can be made as short as less than 10mm in length or as long as 100 mm or more. If long stents are to beused, however, matching length delivery catheter balloons will typicallybe needed to expand the stents into their deployed positions. Longstents, depending on the target vessel, may require curved long balloonsfor deployment. Curved balloons which match the natural curve of a bloodvessel reduce stress on the blood vessel during stent deployment. Thisis especially important in many coronary applications which involvestenting in curved coronary vessels. The use of such curved balloons iswithin the scope of the present invention.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formsdisclosed. Obviously, many modifications and variations will be apparentto practitioners skilled in this art. It is intended that the scope ofthe invention be defined by the following claims and their equivalents.

What is claimed is:
 1. A stent in a non-expanded state, comprising: afirst column expansion strut pair formed of a first expansion strut anda second expansion strut that is parallel to the first expansion strut,the first and second expansion struts being coupled by a substantiallylinear joining strut that is joined to each of the first and secondexpansion struts at a non-perpendicular angle, a plurality of the firstcolumn expansion strut pair forming a first expansion column; a secondcolumn expansion strut pair formed of a first expansion strut and aparallel second expansion strut, the first and second expansion strutsbeing coupled by a substantially linear joining strut that is joined toeach of the first and second expansion struts at a non-perpendicularangle, a plurality of the second column expansion strut pair forming asecond expansion column; and a plurality of first serial connectingstruts forming a first connecting strut column, the plurality of firstserial connecting struts coupling the first expansion column to thesecond expansion column, a first connecting strut in the firstconnecting strut column having a proximal stem that includes curvature,a distal portion with a distal stem that includes curvature and anintermediate portion that couples the proximal and distal portions; andwherein the first expansion column, the second expansion column, and thefirst connecting strut column forming a plurality of symmetricalgeometric cells.
 2. A stent in a non-expanded state, comprising: a firstexpansion column formed of a plurality of pairs of a first expansionstrut and a parallel second expansion strut, the first and secondexpansion struts being coupled by a substantially linear joining strutthat is joined to each of the first and second expansion struts at anon-perpendicular angle; a second expansion column formed of a pluralityof pairs of a first expansion strut and a parallel second expansionstrut, the first and second expansion struts being coupled by asubstantially linear joining strut that is joined to each of the firstand second expansion struts at a non-perpendicular angle; a firstconnecting strut column formed of a plurality of first connectingstruts, a first connecting strut in the first connecting strut columnhaving a proximal portion that includes curvature, a distal portion thatincludes curvature and an intermediate portion that couples the proximaland distal portions, wherein the first connecting strut column couplesthe first expansion column to the second expansion column and includes afirst slant angle formed between the proximal and distal portions.